With advances in semiconductor design and fabrication, the circuit density that can be implemented on a given integrated circuit die has steadily increased. With this increased density, the power consumption and heat generation have also correspondingly grown. This increase in heat requires a design for efficiently removing heat from an integrated circuit die in order to avoid temperature induced failures.
A typical approach to removing heat from an integrated circuit die is to attach a heat sink to the exterior of the semiconductor packaging. A heat sink is commonly understood to increase the dissipation of heat by means of conduction, convection and radiation as a result of the heat sink's high thermal conductivity and relatively large mass and surface area. The package itself is relied upon to provide the thermal pathway from the integrated circuit die to the external heat sink. In a typical embodiment, a die attach material adheres the backside of the integrated circuit die to the package baseplate which may be a leadframe or a plastic or ceramic substrate. The type of material used for the die attach is a function of the package type and performance requirements. Typical materials are epoxy, lead-tin solder and gold alloys.
Unfortunately, such a configuration may result in device reliability failures and other problems. Heat dissipation with this configuration may simply be inadequate for higher power devices. In addition, voids and poor coverage by the die attach layer may cause temperature gradients across the integrated circuit die. These gradients may cause regions of the die to be outside of the optimal operating temperature range, and may also cause mechanical stresses due to non-uniform thermal expansion.
The prior art contains a number of methods for improving the heat dissipation from a packaged integrated circuit die. One such method involves using a flip chip package instead of a wire-bonded package. A flip chip package design has better thermal performance when compared with a wire-bonded device because of the large cross-section and good conductivity provided by the “solder ball” contacts. Other methods involve optimizing external heat sink composition and shape and/or adding a fan to aid in convective cooling. Finally, an epoxy-based die attach may be optimized for thermal conduction by filling the material with metal particles.
Many of these methods are unable to provide adequate cooling capacity for higher power devices. In addition, many of these techniques are not cost effective. For the foregoing reasons, a new design that enhances cooling capacity while staying within the constraints of modern integrated circuit fabrication technology is desirable.